The present invention relates to a method of chromatographic separation of fluid mixtures into fractions and to a chromatograph therefor and may be useful, for example, in the production of pure substances.
Known in the art is a method of continuous separation of fluid mixtures into three fractions by means of a moving adsorbent bed. Such method is described, for example, in U.S. Pat. No. 3,338,031. To a vertical chromatographic column with a descending adsorbent bed a side column is connected by its lower end to the point below the inlet of the fluid mixture being separated; in this side column the adsorbent linear velocity being controlled separately. Separated fractions are collected (as sorbing ability is increased) from the top section of the main column, top section of the side column and from the bottom section of the main column.
This prior art method, however, features an essential disadvantage residing in that, in addition to rather complicated process technology and operation, particle size of the sorbent and, hence, its separating ability are constantly changed due to the friction of the moving sorbent particles against the column walls and against each other.
Known in the art is another method of chromatographically separating a continuously fed fluid mixture of compounds into fractions using stationary columns with a fixed adsorbent bed by means of a chromatograph specially designed for this method. The chromatograph comprises 12 separating columns series-connected into a closed loop and adapted for simultaneously passing two independent gas streams through individual sections thereof. Separated fractions are discharged in the intersections between the columns, while the mixture being separated is continuously delivered into the middle section of one of the columns. The inlet points of the gaseous streams and the mixture of compounds to be separated and outlet points of the separated fractions are simultaneously switched over to the columns in the direction of the gaseous streams to a column length in equal time intervals. (Cf. P. E. Barker and R. E. Deeble, Analytical Chemistry, vol. 45, No. 7, June 1973, 1121).
Also known in the art is a method of chromatographic separation of a continuously fed fluid mixture of compounds into fractions using stationary columns with a fixed adsorbent bed by means of a special chromatograph. This chromatograph comprises stationary columns connected to a circulation circuit, an inlet means for the mixture to be separated, two gas paths and a detector, the columns being divided into three or more groups and connected to three groups of commutation means respectively connecting both gas inlets of the chromatograph with the inlets of said column groups, inlets and outlets of the columns with each other and with the inlet means of the mixture being separated, and with the outlet channels of the chromatograph in such a manner that in any position of the circuit two or more column groups are connected in series into one gas path; said inlet means for the mixture to be separated being connected to the middle section between said column groups, while the remaining column groups are included into another gas path. In equal time intervals, the inlet points of the gas streams and the mixture of substances to be separated and outlet points of the separated fractions are simultaneously switched over to respective columns in the direction of the gas streams to a length of one column group.
Both said last prior art methods and chromatographs therefor have a disadvantage residing in that the mixture is separated into two fractions only, while, to purify the desired product from both less-sorbing and more-sorbing impurities which is a typical problem in such purification, separation of the mixture into three fractions is required. To accomplish this object by said methods, the mixture to be separated should be passed twice through the system, whereby a specific output from a unit sorbent volume in the column is correspondingly decreased.
It is an object of the present invention to provide a method of chromatographic separation of fluid mixtures of compounds into fractions and a chromatograph therefor which ensure continuous separation of a mixture into three and more fractions by means of a circulation separation system using stationary columns.
This object is accomplished by that in the method of chromatographic separation of fluid mixtures of compounds into fractions in accordance with the present invention by means of circulating a continuously fed mixture to be separated within a system of several columns adapted for simultaneously passing two independent fluid streams through separate series-connected sections with synchronically replacing stream inlet and outlet points, the mixture is preliminarily separated, in accordance with the invention, by circulation within a system consisting of at least three separating columns, into two fractions discharged from the column system with separate fluid streams, one of the streams or both containing a preliminarily separated fraction in the form of a mixture of substances is respectively passed through one additional separating column or two such columns, wherein said fraction is separated into narrower fractions or individual components.
In a chromatograph intended for the realization of the method according to the present invention and comprising a system of stationary separating columns flushed with two separate fluid streams, a distributor of said streams between the inlets of the column system, a dosing device and a valve unit connecting outlets and inlets of the columns together, with the dosing device, with fluid outlets, in accordance with the present invention, in the body of the valve unit there are made three channels in the same direction, connected at one end thereof with the inlets of the columns and with the stream distributor outlets and at the other end connected with the outlets of the same columns. In a substantially transverse direction thereto in the same body there are provided three other channels plugged at one end thereof, while the other end of one of these channels is connected to the dosing device, two other ends being connected to the fluid outlets, and at each crossing of one channel over the other branch ducts from both channels are provided opening at the external surface of the body and covered in pairs with membranes thus forming nine membrane valves connecting said channels with each other, each of the channels connecting inlets and outlets of the columns with each other are interrupted under the membrane of the valve connecting said channel to the dosing device; one of the channels connecting the valve unit to the fluid outlets being provided with an additional separating column with a distributor of fractions at its outlet.
Such an arrangement of the chromatograph ensures direct separation of a mixture of compounds into three fractions.
It is abvisable that in the chromatograph for direct separation of a continuously fed fluid mixture into four fractions, in accordance with the present invention, in both channels connecting the valve unit to the fluid outlets separating columns be mounted provided with detecting means and fraction distributors.